Photochromism is a phenomenon that is drawing attention in recent several years and is a reversible action of a compound which quickly changes its color (called color development) when it is irradiated with light containing ultraviolet rays such as sunlight or light of a mercury lamp and resumes its initial color (called color fading) when it is no longer irradiated with light but is placed in a dark place. The compound having this property is called photochromic compound. One of the applications of the photochromic compound may be a dimmer material for lenses of sunglasses.
When used for the above application, the photochromic compound must satisfy the following photochromic properties:    {circle around (1)} Color changes stably when the color development and color fading are repeated (favorably resistance the repetition).    {circle around (2)} Has a small coloring degree in a state of not irradiated with light (has a small initial color).    {circle around (3)} Exhibits a quick fading rate when the irradiation with light is discontinued.
In recent years, further, it has been desired to realize a compound which is capable of developing a neutral tint such as grey, brown or green. The compound that develops such a neutral tint must have two absorption bands (420 to 520 nm and 520 to 620 nm) of nearly the same absorption intensities in the wavelength region of visible rays.
In order to satisfy the above requirements, there have heretofore been synthesized a variety of photochromic compounds without, however, any common nature in their structures.
U.S. Pat. No. 5,783,116 discloses a chromene compound represented by the following formula (A), 
This chromene compound, however, has only one absorption band. Therefore, this chromene compound is not capable of developing a color tone of a neutral tint and, besides, exhibits a slow fading rate.
Further, PCT Patent Application WO00/15628 discloses a chromene compound represented by the following formula (B), 
To satisfy the requirement of coloring spectrum of the above-mentioned neutral tint, this chromene compound develops a neutral tint of brown color while developing a small initial color involving, however, a problem of a slow fading rate.
The present inventors have previously discovered a chromene compound represented by the following general formula (C) among the compounds disclosed in their patent application (Japanese Unexamined Patent Publication (Kokai) 11-154272). 
This chromene compound exhibits a largefading rate. Due to a large difference in the absorption intensity between the two absorption bands, however, this chromene compound is capable of developing a single blue color only.